In the fields of packet-switched networks and computer networking, a traffic engineering term Quality of Service (QoS) refers to the probability of the telecommunication network to meet a given traffic contract. In many cases is used informally to refer to the probability of a packet succeeding in passing between two points in the network within its desired latency period. Basically QoS works by slowing unimportant packets down, or in the cases of extreme network traffic, throwing them away entirely. This leaves room for important packets to reach their destination as quickly as possible.
The numerous communication technologies provide a wide rage of mechanisms to maintain appropriate quality of service. A primitive approach to quality of service problem is generous over-provisioning of capacity so that interior links are considerably faster than access links. In larger scale systems and complex communication environments it is, however, not possible to rely only on such extravagant approach. One method of balancing the capacities is to apply subscriber-based quality of service. Network customers and providers may enter into a contractual agreement (a Service Level Agreement), which specifies in detail the ability of a network/protocol to give guaranteed performance/throughput/latency bounds based on mutually agreed measures. These specifications are mapped into subscriber specific quality of service profiles that are distributed and applied in implementing the communication access.
Advanced communication systems define subscriber-based quality of service system functionalities that are highly sophisticated and enable adjustment of the transmission parameters with local policies in several network domains. As a downside, the resulting complexity of these mechanisms is high and latencies related to signaling are high. Optimized solutions for quick and straightforward subscriber-based quality of service are needed.